Field of the Invention
The present invention relates to ferromagnetic hexagonal ferrite powder.
The present invention also relates to a method of manufacturing the above ferromagnetic hexagonal ferrite powder by a continuous hydrothermal synthesis process, and to a magnetic recording medium comprising the above ferromagnetic hexagonal ferrite powder as the ferromagnetic powder in a magnetic layer.
Discussion of the Background
Conventionally, ferromagnetic metal powders have been primarily employed in the magnetic layers of magnetic recording media for high-density recording. Ferromagnetic metal powders are comprised primarily of iron and the shape of the particles is primarily acicular. In ferromagnetic metal powders, reduction of the powder size and heightened coercive force are sought for high-density recording. These powders have come to be employed in magnetic recording media of various applications.
Ever higher density recording has been demanded of magnetic recording media due to the increasing amount of information being recorded. However, limits to the ability to improve ferromagnetic metal powder to achieve ever higher density recording have begun to appear. By contrast, in ferromagnetic hexagonal ferrite powder, the coercive force can be high enough to permit use even in permanent magnetic materials, and magnetic anisotropy, which is the basis of coercive force, depends on crystalline structure, making it possible to maintain a high coercive force even in fine particles. Further, magnetic recording media in which ferromagnetic hexagonal ferrite powder is employed in a magnetic layer afford good high-density characteristics due to the vertical component. In this manner, ferromagnetic hexagonal ferrite powder is a type of ferromagnetic powder that is suited to achieving higher densities.
Various proposals have been made in recent years to further improve ferromagnetic hexagonal ferrite powder having the above good characteristics (for example, see US2003/0077382A1, U.S. Pat. No. 6,251,474, and Japanese Unexamined Patent Publication (KOKAI) No. 2010-241639, which are expressly incorporated herein by reference in their entirety).